1. Technical Field of the Invention
The present invention pertains to NOR circuit or other logic circuit operating in the current mode.
2. Related Art
FIG. 8 is a circuit diagram illustrating an example of the configuration of a conventional current-mode logic circuit. Logic circuit (10) shown in the figure is a NOR logic element composed of npn transistors Q11-Q14 and resistance element R11.
The base of transistor Q11 is connected to the feed line of control signal VBB, the emitter is grounded, and the collector is connected to the emitters of transistors Q12-Q14. The base of transistor Q12 is connected to input terminal TIN1 of first input signal IN1, the base of transistor Q13 is connected to input terminal TIN2 of the second input signal IN2, and the base of transistor Q14 is connected to input terminal TREF of reference signal VREF of transistor Q14.
The collectors of transistors Q12 and Q13 are connected through resistance element R11 to the supply line of power supply voltage Vcc, and the collector of transistor Q14 is connected to the supply line of power supply voltage Vcc.
Output node NDOUT forms the connecting point between the collectors of transistors Q12 and Q13 and resistance element R11, and its output node NDOUT is connected to output terminal TOUT.
In the aforementioned configuration, when either the first or second input signal IN1 or IN2 is high, transistor Q12 or transistor Q13 turns on, the potential of output node NDOUT is pulled to ground, and the output signal level SOUT goes low.
In this case, control signal VBB is fed from another circuit to the base of transistor Q11, and constant current I flows into the collector of transistor Q11. If the resistance of resistance element R11 is R, the logic amplitude VL of the low-level output is given by the following formula. EQU V.sub.L =R.times.I Numerical formula 1
Usually, when this value is 0.2-0.3 V, the circuit can be used as a logic circuit.
However, in order to realize low power consumption for this circuit, the resistance R of resistance element R11 must be very large.
For example, if VL=0.2 V when I=1 microampere, R=200 kiloohms. It is undesirable to use many such high resistance elements in the conventional IC process from the standpoint of cost and parasitic elements.
An object of the present invention is to solve the aforementioned problems of the conventional technology by providing a type of logic circuit in which the power consumption can be reduced without increasing the size.